People ask me this question, and my reply is, "Whatever you want!" Truth is, SL for educators is a toolkit with some templates. What you do with that is up to you. Here's an example, training paramedics. This took a great deal of time and planning, but as one student writes, it's the next best thing to a real experience.
Problem with SL is, it is very difficult to create learning environments like this. You need scripters (code writers), artists, instructional designers, project managers, testers, etc. Not for the faint of heart - or the lone faculty member with no time to spare.
So mostly in SL you see instructors getting people together for a socially-enriching experience that doesn't tap into the full power of SL.
One approach I tried that seems to be working is to do an initial build for an instructor, then leave the build open for the instructor to build upon. I did this at the Hacienda on Penn State Isle in Second Life. Here's the original build:

It's amazing to see what Gloria Clark, the instructor using that space, has done there. She's added things from paintings to buildings. It's truly amazing. If I had a scripter to lend her, I know she has other ideas she just can't realize at this time. Here's the current build:

Still, the idea of an initial build followed by continuous change and addition seems to be working in this case. I wonder if it's a replicable model?